A recent double-blind, placebo-controlled study investigated the effect of modafinil on cortical excitability in narcolepsy by means of transcranial magnetic stimulation (TMS) and explored the relation between these TMS measures and conventional measures of sleepiness. Electroencephalographic (EEG) low-resolution brain electromagnetic tomography (LORETA) was developed in order to identify brain regions that are involved in neuropsychiatric disorders and are the targets of therapeutic drug action. Modafinil did not influence thymopsychic variables in narcolepsy, but it significantly improved cognitive performance, which may be related to medial prefrontal activity processes identified by LORETA. To bridge the currently wide gap between the neurotransmitter and the behavioral level and to improve temporal resolution up to the millisecond level, it may be useful to study the individual components of event-related brain potentials (ERPs). The ERP study revealed significantly shortened N2 and P300 latencies under modafinil compared with placebo, which reflects an improvement of information processing speed.